One standard procedure for fastening or clamping a metal member to a ceramic member is to drill and tap the ceramic member and to attach the metal member to the ceramic member with screws or bolts. However, difficulty frequently arises from the use of this procedure, because ceramic members break very easily when subjected to unlimited forces by the use of screws, and because ceramic members do not hold threads very well. These problems are compounded when the assembly of the metal and ceramic members must be heated to elevated temperatures, thereby causing the metal and ceramic members to expand at different rates. The thermal stresses thus created in the ceramic member frequently cause it to break. One particular application in which these problems have occurred is in a field-ionization source for a spectrometer which includes a ceramic member held between a base plate and a field plate made of metal. For certain applications, such a spectrometer must be able to withstand temperatures up to 400.degree. C.